b.logrythmik

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Using Policy Injection with ASP.NET MVC and Unity

There are a million and a half articles out there about Policy Injection and the Policy Injection Blocks (from Enterprise Library). Most of them are by my new favorite blogger, David Hayden. If you aren't familiar with Unity, check out these posts first.

The articles span the life-cycle of Unity from before Policy Injection was introduced and some of the actual type names change from article to article, so it wasn't as straight forward as I am going to make it here.

First of all, I didn't want to use a config file - I wanted to configure my policies in the same place I was configuring my dependencies; in the Global.asax code-behind.

It turns out that this is super easy!

Assuming you already have a reference to the Unity library "Microsoft.Practices.Unity", all you need to add is a reference to the "Microsoft.Unity.Interception" library, found in Microsoft Enterprise Library 4.1

You probably already have a place where you are configuring your dependencies:

// Register for Dependency Injection

container.RegisterType<IDataContextProvider, DataContextProvider>();

Now all you need to do is setup the container with an extension that's called 'Interception' then configure each of the Interfaces you want to intercept with Policies. Like so:

// Register for Policy Injection

container.AddNewExtension<Interception>().Configure<Interception>()

    .SetDefaultInterceptorFor<IDataContextProvider>(new TransparentProxyInterceptor());

Now, when you use Unity to resolve your objects, it will detect if any policies are decorated on the interface or the concrete class. If there are policies, Unity creates a transparent proxy object and executes your policies like it does in the Policy Application Blocks. Check out this article to see how to create handlers.

Now you are ready to place your "Policy Attributes" on your classes. Later, I will show you some of my favorite policies I have written for MVC.

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